Tank reactor



Jan. 15, 1952 J DONOHUE 2,582,317

TANK REACTOR I v Filed April 22, 1946 1 5 Sheets-Sheet l I I I -zqb L 118 -55 J5 52 as 58 25 INVENTOB W/W/m J. 00/70/7419 Jan. 15, 1952 w, D N2,582,317

TANK REACTOR Filed April 22, 1946 5 Sheets-Sheet 2 INVENTOR .W/W//WJ00/70/2149 ATTORNEYS Jan. 15, 1952 w. J. DONOHUE 2,582,317

TANK REACTOR Filed April 22, 1946 5 Sheets-Sheet 5 15, 1952 w. J.DONOHUE 2,582,317

TANK REACTOR Filed April 22, 1946 5 Sheets-Sheet 4 INVENTOR 65 w/mwm/w1; BY l m, M 972/6 0 ATTORNEYS w. J. DONOHUE 2,5823] 7 TANK REACTOR Jan.15, 1952 Filed April 22, 1946 5 Sheets-Sheet 5 INVENTOR ATTORNEYSPatentecl Jan. 15, 1952 "I UNITED STATES PATENT OFFICE TANK REACTORWilliam J. Donohue, Aspinwall, Pa.

Application April 22, 1946, Serial No. 663,971

6 Claims.

1 The invention relates to conducting continuous reactions between aliquid and another material such as a solid or immiscible different pliquid or gas, by the general method of alternately mixing the materialsinto a suspension and separating them in stages. The principal objectsof the invention are to improve the efliciency of such method so as toavoid short circuiting in the mixing steps and thereby provide moreperfect control of the mixing time, and to provide apparatus in whichthese improvements may be 'achieved. More specifically, my apparatus andmethod insure in the mixing step co-current travel of the liquid andsuspended particles. throughout long spiral paths, of controllablelength and with controllable velocities. This is effected by the novelmanner in which the materials are progressed from stageto stage, andparticularly by certain improvements in apparatus adapted to efiect suchtreatment. The appara tus may be used with little or no variation forliquid-liquid treatment such as solvent de-waxing of oils or acidtreatment of mineral oils, for

liquid-gas treatment such as absorption, and for liquid-solid treatmentsuch as leaching, extraction, or liquid causticizing. While my methodand apparatus may beused for carrying out various processes, they arespecially suited for the causticizing of a solution of a metal salt,such as sodium carbonate by treatment with calcium hydroxide to producea solution of sodium hydroxide and a precipitate of calcium carbonate.In this application, the liquid and solid entering into the reactionflow through the apparatus in the same direction at all times. In otherinstances, countercurrent flow from stage to stage may be provided.

In my co-pending application Serial No. 620,898, filed October 8, 1945,now Patent No.

2,539,732, I show and describe apparatus similar,

and in some respects identical, to the apparatus of the presentapplication; but the invention of that application not claimed hererelates rather broadly to the manner of progressing the solids andliquids being treated, the structure whereby the compartments areisolated and sealed from one another during shutdown, and otherimprovements not claimed herein.

In a preferred embodiment, my apparatus comprises a reaction vessel,such as a tank, having a plurality of vertically spaced floors therein.Alternate floors have outlets for descending material at the peripheryand at the center, respectively. The spaces above the floors havingperipheral outlets serve as agitation compartments and the spaces abovethe other floors constitute retention or settling compartments whereinthe reaction products and the solid material being treated are separatedfrom the unreacted treating liquid. The agitation compartments areprovided with tangential nozzles adapted to cause a gentle agitation ofthe materials contained therein. A liquid (or in some cases a gas) isintroduced through the nozzles, causing the materials to rotate aboutthe axis of the tank. Solids (or other material immiscible with thefluid introduced through the nozzles) enter at the center, and travelwith the liquid through a long spiral path to the peripheral outlet intothe adjacent settling compartment. All the compartments may have rotarymeans for sweeping solids settling on the floors towards the outlets.When the apparatus is to be used for causticizing sodium carbonatesolution or so-called "green liquor by reaction with lime, I providemeans at the top of the tank for slaking the lime, CaO, by the Water ofthe entering solution to produce calcium hydroxide which reacts directlywith the sodium carbonate.

In the causticizing of green liquor, the desired end product is usuallythe sodium hydroxide solution and an important factor in quality thereofis its clarity or freedom from suspended solids, such as minuteparticles of calcium carbonate. At the same time, it is desirable to useas small an excess of lime as possible over the amount theoreticallyrequired for reaction with all the sodium carbonate solution. A certainamount of excess lime is necessary, of course, to cause the reaction toproceed to a conclusion within a reasonable time. Agitation of thereacting materials tends to expedite the reaction but also leads tofragmentation of the precipitating particles which causes the liquidproduct to be cloudy rather than clear by reason of the presence ofsmall suspended particles. The fineness of the calcium hydroxidedelivered to the reaction chamber is also a factor in the size of theparticles of the solid reaction product. The clarity of the product isalso afiected by the amount of lime which remains unconsumed afterreaction has been completed. In accordance with my invention, I utilizeliquid jets for obtaining a gentle agitation sufficient to bring allportions of the reacting materials into contact with each other and atthe same time avoiding such violent agitation as would prevent thegrowth of large crystals of precipitate which will settle rapidly in theliquid reaction product. The liquid re- --partments I], I8, I 9 and 23.

of. ".tral holes therein affording outlets from the action productshould have as high a concentration as possible. This depends upon thecompleteness to which the reaction is carried out.

While the invention assists in obtaining calcium carbonate particles ofrelatively large size, the size may, of course be controlled by Varyingthe above-mentioned factors to include fine material in case this isdesired. It is recognized that in some paper plants recovery of a finecarbonate to be used as filler ispreferred to coarse carbonate to bereburnt to produce the causticizing lime; and the invention is adaptedto produce such crystals as well as large ones.

For a complete understanding of the invention, reference is made to thedrawings illustrating a preferred embodiment and a' modification, bothof which are described in detail herebelow. In the drawings,

Figure 1 is a central vertical section through a reaction apparatusaccording to my invention;

Figure2 isa plan view of the apparatus with the top-removed;

Figure 3 is a horizontal section taken along theplane of line III-III ofFigure 1;

Figure 4 is a diagrammatic view showing the apparatus in centralvertical section with most of .the mechanical details omitted toillustrate the flow of material therethrough;

Figure 5 is a horizontal section taken along the-planeof line V-V of.Figure 4, with parts omitted;

Figure 6 is an elevation of a modified form of apparatus;

Figure '7 is a central vertical sectiontherethrough;

Figure 8 is a horizontal section taken along the plane of line VIII-VIIIof Figure 7;

"Figure 9 is a horizontal section taken along the planeof line IXIX ofFigure 7;

"Figure 10' is a portion of Figure '7 toenlarged 'scale illustrating adetail; and

Figure 11 is a View showing alternative construction of 'a part of theapparatus.

Referring now in detail'tothe drawings and,

for the present, to Figures 1 through 4, theapparatus of my inventioncomprises a cylindrical tank l3. including a side wall II, .a top l2 anda bottom l3. Vertically spaced floors l4, l5 and lfitogether with thebottom I3 define a-plurality of alternate agitation and retention com-The' floors M and I6 terminate short of the wall I! affording peripheraloutletsfrom the compartments-H and I9. These floors may be supported onbrackets orbeams (not shown) secured-to 'the-* side wall ll of the tankIf! and extending inwardly there- The floor i5'and the bottom 3 havecencompartments ISandsZlQ. The outlet'from the compartment '|,8 includesa neck 2| depending from thefloor l5 and radial baffles orswirlstop-,pers 22 extending inwardly therefrom.

-A conical neck 23 extends downwardlyvfrom the opening i-nithe bottom I3and has a dis- :chfillgc. pipe .24 connected thereto.

The apparatus is provided with -a vertical shaft 25'journaled centrallythereof on a thrust .32 provided With plows 33 spaced along the .lengththereof.

The plows are-simply plates secured to the arms in such angular relationas to cause radial movement of solid material on the compartment floorstoward the outlets, the lower edges of the plates being spaced a shortdistance above the floors.

Tangentially directed nozzles 34 are mounted in the agitationcompartments l1 and l9 by any convenient means and are adapted, whenconnected to a source of treating liquid under suitable pressure; tocause circular movement of the material. in the compartments. A trough35 in the retention compartment |8 permits a portion of the treatingliquid to be withdrawn for recirculation to the agitation compartmentl9. In the retention compartment 20 I provide a similar outlet trough 36which is used for starting the apparatus as will be subsequentlyexplained. Normally liquid in compartment 20 is not .drawn on" throughtrough 36, valve 36a (see Figure 4) ordinarily being closed; but thesuspension of calcium carbonate in causticizedeliquid is continuously,drawn off throughpipe 24.

The nozzlesfor introducing fluid tangentially may be aplurality ofsmall. nozzles 34 as inFigures 4 and 5 or a single larger, nozzle'34aasin Figurelll, in which fluid from a relatively large pipe is deflectedby. means of a vplateformed as a segment of a circle. Any means adaptedto impart to the liquid a relatively large tangential velocity may beused. The spiral path results as the combined effect of the relativelylow radial velocity and relatively high tangential velocity. The outwardflow ,of solids may'be accelerated somewhat by centrifugal force; and atany rate thesolids are not required to flow counter to this force.

The peripheral outlets from compartmentsil'! and I9 are segmentalpassages between the tank wall and depending skirt |4a or upstanding rim|6a. The passages are separated by vertical baffies or'swirl stoppers|4biand [6b, which arrest the rotary motion of the materials and permitthe suspension to flow out substantially radially into thecompartmentbelow. An outlet'38 for solid rejects leads downwardly, from.the floor It through the side wall of the tank'and is provided with anupwardly directed nozzle 39.

When the apparatus is'to be used for causticizing. green liquor, Ipreferably provide a lime slaking compartment 40 in thenpper part of thetank. To this end, arevolving circular*tray4| having-a peripheralflangeor wal1'42 is mounted 'on radial arms 43 extending-from the shaft25. A lime inlet pipe 44 extends'through the top l2. Stationary plows45a and 4512 are mounted on radial beams 46 extendingacross'the top |2asshown in Figure 2. Inlet nozzles 4! extend through the top |2 forspraying green liquor'on the lime delivered'to the tray 4| throughzthepipe 44. The tray 4| hasa centralopening 4m providing an outletformaterials into'the compartment below.

The operation of the apparatus described above may best be explained byreference to'FigureA which illustrates certain auxiliaries, such as achain and bucket elevator 48 and pumps 49 and 50. vLime is delivered bythe elevator 48 to the pipe 44 and discharged onto the tray. Greenliquorisdeliveredby the pump 5D,.through a pipe line 5| to thenozzles41. Thellevelofliquidin the tankvmay .be maintained adjacent the upperedge of the flange 42 of the tray 4|, as indicated by the chain line 52ortslightly belowthe-tray M as indicated by the chain line 53.As-thetray i .4| revolveswith'the shaft 25, the lime thereon is movedradially by the plows 45 and is subjected to hydration by the watercontent of the green liquor. The plows 45a move the lime radiallyinwardly and the plows 45b outwardly, so as to turn the lime over andwork it back and forth as the liquid is applied. The pitch of plows 45a,however, is somewhat greater than that of plows 45b, so that the inwarddisplacement is greater than the outward displacement, and the materialis gradually progressed from the circumference of the tray to thecentral outlet M a. This effect may, of course, be achieved by anyequivalent means, such as providing plows 45a of greater width than 45bor in a greater number, instead of at steeper pitch. The heat evolved isconfined in the tank Ill and absorbed by the liquor therein. A ventstack 54 has a spray nozzle 55 therein to which a supply pipe 56 isconnected. The pipe 56 branches from the pipe 51 supplied by the pump50. The spray produced by the nozzle 55 collects lime dust resultingfrom the slaking operation and returns it to the tray 4| as well as mostof the heat in the vapor passing to the vent.

When the lime has been moved radially of the tray 4| to the centraloutlet, it has been converted for the most part tocalcium hydroxide anddescends with the excess green liquor into the agitation compartment H.The nozzles 34 therein supplied with additional green liquor throughpipe 51 cause a spiral circulation of the calcium hydroxide and greenliquor together as a suspension'fiowing towards the circumference.

The circulation maintains suiiicient velocity to hold the lime particlesin suspension for reaction with the liquid, and provides a long spiralpath through the-compartment by which short-circuiting is avoided,detention time is controlled, and the causticizing reaction caused toproceed in the desired manner. Heavy reject material such as sand andlarge lumps which may settle out on the floor I4 are swept toward theperiphery thereof by the plows 33. In the retention compartment l8, thesuspension is separated into solid and liquid portions by permitting thesolid particles to settle through the reacting liquid. Partiallycausticized liquid is drawn off from this compartment through trough 35by pump 49 and recirculated through the nozzles 34 in compartment l9.

- The solid particles settling on the floor l are moved toward thecentral outlet thereof by the plows and are again mixed with andsuspended in reacting liquid in compartment I 9 in the above describedmanner; the sand, heavy rejects, and any impurities mixed therewithsettle on floor l E and are swept toward the rejects outlet 38 by theplows. The reaction products, sodium hydroxide solution with calciumcarbonate particles sus-' pended therein, flow through thecircumferential passages to the final retention compartment 20. Thenozzle 39 in the outlet 38 may be connected to the outlet of pump 49 todeliver recirculated reacting liquid against the outflow of rejects,thus flushing them of fine particles, further to reduce the amount oflime discharged unused.

Liquid outlet 36 is provided in compartment for starting up only. Atthis time the tank is filled with a solution containing sodiumcarbonate, and lime alone is fed for a time to the slaking tray. Valve36ais then opened and the liquid from compartment 20 drawn 01f by pump50 to the nozzles 41; and the apparatus thus operated for several hoursuntil desired operating equilibrium is reached. Valve 36a is thenclosed, and the pump 50 thereafter used to provide supply of greenliquor instead of merely recirculating liquid within the apparatus.

The agitation produced in the compartments I! and 18 by the nozzles 34is sufficient to accelerate reaction between the hydroxide and the greenliquor but not sufficient to break up the calcium carbonate particlesresulting from crystal growth as a result of the reaction between thesolid and liquid. As a result, in later settling and washing operationsthe carbonate particles settle rapidly leaving a sodium hydroxidesolution of a high degree of clarity. The agitation produced by thenozzles is suflicient to hold the largest carbonate particles insuspension in the compartments I! and i9, but not great enough to causefragmentation of the carbonated crystals. The heavy hydroxide particlesand impurities are not in suspension but sink promptly to the floors ofthe compartments and are pushed therealong toward the outlets. This isaided by the swirling action of the contents of the agitationcompartments resulting from the tangential adjustment of the nozzles.

During the travel of the solid and liquid through the agitationcompartment, the heaviest carbonate particles are held in motion closeto the floor while the lighter carbonate particles and still lighterunreacted hydroxide particles are successively higher in thecompartment. This stratification is desirable because it keeps theunreacted hydroxide in constant contact with the least causticizedliquor. It is also helpful in holding down the amount of excess limethat must be supplied. A relatively small proportion of the enteringliquor is sufiicient to produce the desired swirl in the agitationcompartments. The balance of the green liquor flows gently out into thecompartment from that above.

It will be noted that the materials spill over 1 rim Eta from thechamber [9 at a level well above the floor It, thus only materialactually in suspension in liquid is allowed to pass into the compartment20. The rapidly settling unused hydroxide particles and impuritiescollect on the floor l6 and are swept therefrom into the outlet 38. Theagitation of the liquid in compartment [9 should be sufiicient tomaintain the carbonate particles suspended but not enough to stir up thesolid rejects, i. e., impure lime lumps,-

contact is prevented by the long spiral path which the reactingmaterials follow in passing through the agitating compartments. Shortcircuiting is further avoided by recirculating the lightest or leastcausticized liquor from the retention compartments to the agitationcompartments where unreacted hydroxide is available. An extended periodof time is available for reaction between the solid and liquid as theypass through the several compartments and this reduces the amount ofexcess lime required. Before any material is rejected from the ssytem,it is well worked over and all possible good lime is utilized. Thescrapers that serve to clean the various compartment floors, do nottouch the floor. Consequently, there is a half inch or so' of-clearance.

between the floor and the scraper which will fill with sand and othersmall reject material. This rough surface actsto scrape and scour theheavier and larger lime lumps that are moved across it, and by the timethe lump is discharged from the secondary agitation compartment, thereis little, if any, recoverable lime value remaining.

There are no fast moving mechanical parts in this apparatus that come incontact with abrasive solids. In consequence there is a minimum ofabrasive wear with its always attendant replacement. Because allagitation is developed through the medium of pumped liquor, the use ofquickly worn-out, mechanical agitation equipment is totally avoided.Furthermore, all liquor used to secure agitation is clear liquor andcontains no abrasive solids. This helps keep pumps from wearing out.

By the provision of the slaking compartment 40 and the revolving tray5!, it is possible to use quicklime, CaO, as it comes from the kiln.Lime slaking for causticizing has heretofore generally been done inseparate apparatus, and the product. pumped to the causticizer. It hasalways been necessary to include with the slaker some provision forremoving foreign materials and large lumps because a purified lime istoo expensive. In the apparatus, economy in the consumption of lime isobtained by Working over the solid material while it is in contact withthe liquor: being treated, and removing rejects after causticizinginstead of before causticizing. This prevents the impurities frompassing through as adulterants to the calcium carbonate sludge,yetpermits all usable values to be reclaimed from lumpy materials suchas lime. The tray 4| provides a steady feed of slaked lime and the heatevolved in thisoperation is conserved as well as the lime dust usuallygiven off. As to its more general utility, the revolving tray may besuitable for feeding and preliminary treatment in a bulk state ascompared to a suspended state, any solid substance subsequently to bereacted with liquid in suspension. Other examples might be included,such as dosing various mineral substances with acid or alkali prior tosubsequent treatment, the preliminary mixing of caustic with rubber tobe devulcanized, or any instance where the solids mass is required to befed, treated with liquid and worked over continuously.

My apparatus and method thus provide a combination of agitation andredistribution of the solid and liquid constituents as they progressthrough several compartments in series. The agitation is effected by jetmeans whereby the liquid tobe treated isintroduced at an optimum levelin a stratified, swirling cylinder of liquid and solids insuspension,the swirling being effected by the tangential setting of the jets withrespect to the vertical axis of the apparatus. The optimum. level isthat at which the suspension is rich in calcium hydroxide, the densercalcium carbonate being principally below this level. Redistribution isefiected by drawingoif the Weakest portion of the partially reactedliquor in a quiet intermediate compartment, and introducing it againthrough jets in a lower compartment at a similar optimum level richestin unreacted hydroxide. It is essentially merely a repetition of thefirst contacting step, with a separation of liquid and solid constituentbetween steps. The rate of circulating liquid handled in theredistributing steps, however, is subject to control, andmay be equalto, less than, or even greater than the netdownward flow of liquidthrough the apparatus. In causticizing, this rate would ordinarilybeless than the net liquid flow, being a suitable portion thereof, e.g., most of t'heliquor below a nominal per cent of causticity, therebeing some liquor equal to or exceeding this causticity produced in thefirst-stage of th-eap paratus. In this case, the remainder of the liquidflows with the solids downwardly through the central opening'from theretention compartmentto the secondary agitation compartment. Iftheliquid is pumped to the jets at the same rate'asthe net downward flow,nothing but solids settling through quiet liquid passes through thiscentral opening. net flow rate, there is an upward flowof liquidsthrough the central opening countercurrent to the downward flow of thesolids, in which case the upward liquid velocity may not exceed suchvalue as will carry the solids also upward; and

prevent their discharge into the secondary agitation compartment. Itshould be noted here that, if desired, vertical bafiles or swirlstoppersmay be provided in this opening.

In the causticizing apparatus described above. the reacting solid andliquid traverse the apparatus in the same direction. The invention isalso applicable to apparatus in which countercur-- rent flow of thesolid and liquid occurs. Figures 6 through 10 illustrate such anapparatus whichis generallyv similar to that already described. Theapparatus there shown comprises a tank 60' having a side Wall 6 I, a top52 and a frusto-conical bottom 53. partments by vertically spaced floors64 through 15. numbered floors terminate short of the wall 6| affordingperipheral outlets for descendin material. Floor 66 and the subsequenteven numbered floors have central outlets similar to those from thefloor 15 of the causticizer of Figures 1 through 5. The floors define amixing compart ment T6 at the top of the tank, settling compartments T!and I8 therebelow and additional mixing and settling compartments 19through 88, the mixing compartments being those with odd numbers.

A vertical shaft 89 disposed centrally of thetank is supported on athrust bearing 90 and is journaled in guide bearings 9i and 92. Thebearing 99 is suspended in a structural frame 93 on top of the tank. Theshaft is driven by a motor 94 through reduction gearing 95 and acoupling- 96.

on the several floors toward the outlets.

The apparatus of Figures fi'through 1 0 is well delivered by a screwconveyor M2 to a press for removal of the solvent absorbed thereby. Theliquor from the press is returned to the tank through an inlet I03 tothe mixing compartment 8?. I

As in the case of the causticizer of Figures 1 through 5, agitation ofthe solvent and material to be extracted is produced by nozzlesdischarging the liquid tangentially into the mixing If the pumping rateexceeds the The tank is divided into com-- The floors 64, $5 and theremaining odd Radial arms. 9'! on the shaft are provided with plows 98for radially moving solids settling compartments. Liquid is alsowithdrawn from the settling compartments and recirculated through theprior stage mixing compartment or compartments thereabove.

The mixing compartments I6, I9, BI, 83, 85 and'8'l are provided with jetagitation means I04 which enter through the partitions forming thefloors of the above-mentioned compartments, the piping thereto beingdisposed in the compartment immediately therebelow. As shown in Figures9 and 10, the agitation means 104 comprises nozzles I08 directedupwardly from a manifold Il-through the floor of mixing compartment. Theends of the nozzles are flush with the floor level and are so formed, asshown in Figure 10, that they discharge in a generally horizontaldirection tangentially of the tank and with a slight upward deflection.It will be apparent that this causes a spiral movement of the materialin the mixing compartment-s, providing sufficient agitation to cause themeal to be suspended in the solvent and providing a long path throughwhich solvent and meal particles travel co-currently at each mixingstage. The suspension flows downward continuously through thecircumferential passages and radially into the separating or settlingcompartments, bafiles 65b arresting the rotary motion established in themixing compartments.

Compartments 11, I8, 80, 82, 84, 86 and 88 are the settlingcompartments, and each is provided with collecting trough I located nearthe center, from which separated liquid is withdrawn, and scrapers formoving th solids inwardly towards the solids outlets. The two uppermostsettling compartments (1! and 18) are operated in parallel to effectfinal clarification of the extract or miscella, the liquid outlets I05therein being connected through pipes IN and H6 to the overflow boxII'I. These thus provide large combined floor area for settling and lowliquid velocity, thereby producing miscella of good claritysubstantially free of suspended solids. Coarser particles descenddirectly through the circumferential passages to compartment 18,bypassing compartment 11. Such fines as flow with the liquid intocompartment 11, settle out on the floor thereof and are plowed radiallyoutwards over the edge of the floor to mingle with and become entrainedby the coarse material "and pass into compartment I8, where the plowsmove all the settled solids towards the central outlet. Bafiles 22 inthe throat of this outlet arrest any vortex which might otherwiseprogress upwardly from mixing compartment I9, and insure the minimum ofdisturbance in the settling compartment I8. Separation in the othersettling compartments need not be so thorough, as it is primarily toprovide countercurrent flow from stage to stage, and single compartmentsat each stage are generally sufficient. The progress of the extractingliquid will probably be made clearer by describing the apparatus herebeginning at the bottom, where the solvent is introduced, and proceedingupwardly through the machine.

The inlet I00 is connected. to the manifold I01 in the compartment 88.The inlet I03 may also be connected to the same manifold. The freshsolvent is thus introduced in the lowest mixing compartment 81. partment88 is withdrawn through trough I05 therein and a radial pipe I08 by apump I09 and delivered through a pipe IIO to the manifold I01 incompartment 86 and thence through the floor into compartment 85. Thepump I09 is driven Liquid in the settling com- .the side of the tank.Pumps II2 through II5 similarly withdraw liquid from the settlingcompartments 86, 84, 82 and and deliver it to the manifolds incompartments 84, 82, 80 and H for discharge in the form of tangentialjets into compartments 83, 8!, 79 and 16. The trough I05 in compartmentsI? and I8 are connected by pipes NH and H6 to an overflow box Hi, fromwhich the miscella is removed from the apparatus.

It will be apparent from the foregoing that the mix-settle type ofcountercurrent extraction apparatus of Figures 6 through 10 is adaptedto receive the material to be extracted at the top thereof andintroducing the extracting solvent at the bottom. By a process ofsuccessively agitating the solvent with the material to be extracted inthe several compartments, with opportunity for settling betweensuccessive agitations and recirculation of the solvent between stages,the solvent becomes progressively more concentrated with the solublecontent of the material being extracted and is eventually taken offthrough the outlets WI and H6 or more if necessary. At the same time,the material being extracted descends progressively through the severalstages of mixing and settling and is finally discharged by the screwconveyor I02 to the press. By this countercurrent operation, the freshsolvent is brought into contact with the solid material having the leastremaining soluble content while the more concentrated solvent in theupper portion of the tank has contact with the solid material having themaximum soluble content. It will be understood that the tank is normallyfilled with material to a level adjacent the top 62 and that theconcentration of the soluble content of the material being extractedincreases progressively from the bottom of the tank to the top. Theapparatus in the form illustrated in Figures 6 through 10 ischaracterized by advantages similar to those of the causticizer inFigures 1 through 5 which have already been enumerated. The extractorutilizes jets of solvent formed by tangentially directed nozzles toeffect the desired gentle agitation of the solid and solvent. The liquidand solid move slowly through the apparatus from stage to stage inopposite directions, the liquid being circulated upwardly'by pumps andthe solid settling by gravity, while the action is co-current in eachtreating stage. Only a slight pressure differential exists betweensuccessive stages and the flow of liquid is thus relatively slow andfree from excessive turbulence.

The foregoing illustrations have described applications where thesuspension on separating causes settling of solids or immiscible liquidsto the bottom of the various compartments. If the suspended solid orfluid particles are lighter than the liquid, the separation takes placein the reverse or upward direction. It is within the scope of thepresent invention to operate in either manner, and where desirable toenter solids at the bottom and solvent at the top and to providescrapers cleaning the roofs of the various compartments instead ofcleaning the floors as shown and described in the specific examples.

Although I have illustrated and described but two preferred embodimentsof the invention, it will be recognized that changes in the details ofthe construction disclosed may be made without departing from the spiritof the invention or the scope of the appended claims.

I claim:

1. Causticizing apparatus comprising a cylindrical tank having aplurality of vertically spaced floors, alternate floors havingperipheral and central outlets, respectively, and defining agitationcompartments above the floors with peripheral outlets and retentioncompartments above the floors with central outlets, rotary means forsweeping solids settling on said floors toward the outlets, tangentiallydirected nozzles in said agitation compartments, and means for supplyingtreating liquid to said nozzles, a floor above the uppermost agitationcompartment providing a slaking compartment, the lowermost agitationcompartment having an upwardly extending flange at the edge of itsperipheral outlet and a second outlet leading from the floor of thecompartment adjacent the flange out through the tank whereby solidrejects may be removed from the tank by the rotary means in thecompartment.

2. The apparatus defined by claim 1 in which said rejects removing meanshas a nozzle in said outlet discharging liquid opposite to the flow ofrejects through the outlet.

3. Causticizing apparatus comprising a cylindrical tank having aplurality of fixed vertically spaced floors, alternate floors havingperipheral and central outlets, respectively, and defining agitationcompartments above the floors with peripheral outlets and retentioncompartments above the floors with central outlets, rotary means forsweeping solids settling on said floors toward the outlets, tangentiallydirected nozzles in said agitation compartments, and conduits forsupplying treating liquid to said nozzles from the upper portions of thesettling compartments, a fioor above the upper agitation compartmentproviding a slaking compartment, a shaft extending through said floors,said sweeping means and said slaking compartment floor being mounted onsaid shaft, stationary sweeping means cooperating with saidlast-mentioned floor, and means for removing reacted mixture from thelowermost agitating compartment, said agitating compartment also havingan upwardly extending flange at the edge of its peripheral outlet and asecond outlet leading from the floor of the compartment adjacent thefiange out through the tank whereby solid rejects may be removed fromthe tank by the rotary means in the compartment.

4. Apparatus for continuously treating solids with liquids comprising acylindrical tank having a plurality of fixed vertically spaced floors,alternate floors having peripheral and central outlets, respectively,and defining agitation-compartments above the floors with peripheraloutlets and retention compartments above the floors with centraloutlets, tangentially directed nozzles in said agitation compartments,means for sup plying treating liquid to said nozzles and flangesextending downwardly at the edges of said outlets whereby the amount ofmotion of materials in the agitation compartments which is transferredto the settling compartments is reduced.

5. Apparatus as defined in claim 4 in which said nozzles dischargethrough the floors of the agitation compartments from below andterminate substantially flush with said floors.

6. Apparatus for continuously treating solids with liquids comprising acylindrical tank having a plurality of fixed vertically spaced floors,alternate floors having peripheral and central outlets, respectively,and defining agitation compartments above the floors with peripheraloutlets and retention compartments above the floors with centraloutlets, tangentially directed nozzles in said agitation compartments,means forsupplying treating liquid to said nozzles, and downwardlyextending flanges at the edges of the outlets of the agitating andsettling compartments and radial flanges extending inwardly from theflanges around the central outlets whereby the amount of motion ofmaterials in the agitation compartments which is transferred to thesettling compartments is reduced.

WILLIAM J. DONOHUE.

REFERENCES CITED The following references are of record'in the fileof'this patent:

UNITED STATES PATENTS Number Name Date 1,220,995 Schafier Mar. 27, 19171,231,707 Christensen July 3, 1917 1,308,184 McAfee July 1, 19191,678,787 Remick July 31,1928 1,691,511 Bates Nov. 13, 1928 1,810,125Brooks et al June 16, 1931 1,815,646 Bates etal July 21, 1931 1,978,536Jeavons et al Oct. 30,-1934 2,007,799 Gloersen July 9,1935

